15desaturases

15-desaturases, or delta-15 desaturases, are enzymes that introduce a cis double bond at the Δ15 position of fatty acyl chains. In many organisms they convert linoleic acid (18:2 Δ9,12) to alpha-linolenic acid (18:3 Δ9,12,15), a key step in omega-3 fatty acid biosynthesis.

Biochemical features: They are membrane-bound, non-heme di-iron enzymes located in the endoplasmic reticulum or plastids. The reaction requires molecular oxygen and electrons from NADH or NADPH, typically supplied via a cytochrome b5 system. Conserved histidine-rich motifs coordinate the iron at the active site, enabling the desaturation reaction.

Distribution and role: Delta-15 desaturases are found in higher plants, many algae, fungi, and some bacteria. In plants they enable production of polyunsaturated 18:3 fatty acids that contribute to membrane fluidity and signaling. In animals, conversion to longer-chain omega-3 fats proceeds through multiple steps, and alpha-linolenic acid (ALA) must be obtained from the diet in the absence of endogenous synthesis.

Genetics and applications: Plant genes such as FAD3 (endoplasmic reticulum–localized) and FAD7/FAD8 (plastid-localized) encode Δ15 desaturases. Biotechnological efforts aim to alter delta-15 desaturase activity to raise omega-3 content in crops or microbial systems, with implications for nutrition and industrial biotechnology.